The purpose of this study is to explore developmental differences of understanding prosocial lies focused on moral judgement and emotional understanding among 6 and 7-year-old children. The study was conducted on 65 pre-school children (aged between 6 to 7), who attended kindergarten in Seoul and Gyeonggido. The participants were shown an illustrated story having six situations; the preschoolers had to comment on the story. They were asked to make moral judgements and emotional reasoning in antisocial and prosocial situations. The study also determined the relationship between the results of two factors. First, the results revealed that the children could determine the “wrongs” in an antisocial lie situation; however, they also made similar judgements in a prosocial lie situation. This demonstrates that aged between 6 to 7 children, are too immature to make moral judgements in a prosocial lie situation. Second, six and seven year old children, had a better emotional reasoning than moral evaluation in prosocial lie situations. This means that the development of empathetic skills precede the development of moral values. Moreover, as children grow, their reasoning ability improves; a case in point would be, a seven-year-old girl who predicted emotions in a prosocial lie situation much better than younger children did. Finally, the children who scored the highest in emotional reasoning also displayed good moral judgement. This implies that as the prediction ability of emotional reaction develops, the child acquires ability to discern right from wrong in a prosocial lie situation.